FXUS62 KGSP 070530
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1230 AM EST MON DEC 7 2009
.SYNOPSIS...
AN AREA OF HIGH PRESSURE WILL SLIDE OFF THE EAST COAST TODAY AS A
FAST MOVING COLD FRONT CROSSES THE FORECAST AREA. HIGH PRESSURE WILL
THEN RIDGE DOWN THE EASTERN SEABOARD LATE MONDAY NIGHT AND EARLY
TUESDAY AS MOISTURE SPREADS ACROSS THE SOUTHEAST STATES FROM THE
WEST. A STRONG AREA OF LOW PRESSURE WILL DEVELOP OVER THE MOUNTAIN
WEST TODAY AND TUESDAY AND THEN MOVE INTO THE OHIO VALLEY ON
WEDNESDAY...PUSHING A COLD FRONT ACROSS THE SOUTHERN APPALACHIANS.
&&
.NEAR TERM /THROUGH TODAY/...
ONCE THE DENSE CIRRUS OVERCAST EVACUATES THE AREA...WHICH ACCORDING
TO IR IMAGERY/MODEL TIME HEIGHT SECTIONS...SHOULD OCCUR AROUND
06Z-ISH...WE WILL SEE NEARLY IDEAL RADIATIONAL COOLING CONDITIONS
BECOME ESTABLISHED. WITH THIS IN MIND...MIN TEMPS WILL BE LOWERED
2-3 DEGREES IN MOST AREAS. ALTHOUGH LOW CLOUDS ASSOCIATED WITH
ATLANTIC MOISTURE ADVECTION WILL SKIRT THE SOUTHEAST QUARTER OF THE
CWFA EARLY MONDAY...IT APPEARS THIS MAY NOT HAPPEN UNTIL AROUND
SUNRISE...PROBABLY NOT SOON ENOUGH TO HAVE A HUGE IMPACT UPON LOW
TEMPS. OTHERWISE...NO CHANGES OF NOTE WILL BE REQUIRED TO THE
FORECAST.
DEEPER MOISTURE LOOKS FAIRLY SPARSE THROUGH TOMORROW. SLIGHTLY
BETTER RH SHOULD ARRIVE FROM THE W DURING THE AFTN HOURS MONDAY...
WITH SLIGHT CHANCE POPS FOR SHOWERS IN THE MTNS. CHILLY MINS IN THE
20S AND LOW 30S ARE EXPECTED OVERNIGHT...WITH COOL MAXES IN THE 40S
TO LOW 50S ON MONDAY.
&&
.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
AS OF 200 PM SUNDAY...WENT WITH A MODEL BLEND...AS GUIDANCE IN
GENERAL AGREEMENT ON EVOLUTION OF MIDWEEK CENTRAL CONUS STORM.
A POTENT SRN STREAM SHORTWAVE INVOF THE DESERT SOUTHWEST WITH DEEP
SFC LOW...WILL TRACK EASTWARD INTO THE SRN PLAINS STATES BY TUESDAY
EVENING. MODEL CONSENSUS PLACES THE LOW INVOF KS/OK BORDER 00Z
WED...AND TRACKS IT NEWD TO INVOF LAKE HURON BY 00Z THU. AN UPSTREAM
SFC HIGH IS PROGGED TO MIGRATE FROM UPSTATE NY TO LABRADOR DURING
THIS TIME FRAME. A HYBRID CAD LOOKS TO SET UP ACRS THE PIEDMONT FROM
VA TO ERN GA BY TUESDAY EVENING...AS PRECIP BREAKS OUT ACRS MUCH OF
THE SOUTHEAST STATES IN PERSISTENT STRONG LLVL WAA FLOW. THE PRECIP
SHOULD BE IN FORM OF RAIN...AS 850-700 MB THICKNESSES RISE
SIGNIFICANTLY...AND TEMPS SETTLE MAINLY IN THE 40S TO MID 50S.
SYNOPTIC MID-UPR LVL FORCING WILL BE MODEST AT BEST...AS MAIN
Q-VECTOR CONVERGENCE AND JET DYNAMICS WILL BE NORTHWEST OF THE AREA.
WITH THAT SAID...I MADE ONLY MINOR ADJUSTMENT TO POPS...AS TIMING OF
LOW-MID LVL LIFT IS BECOMING MORE CERTAIN. POPS RAMP UP TO
CATEGORICAL CWA-WIDE BY TUES EVENING...THEN TAPER OFF WEST TO EAST
AFTER DAYBREAK WED AS DRY SLOT AND COLD FRONT PUSH THRU FROM THE
WEST. QPF SHOULD STILL BE GENEROUS...AS GULF WILL BE WIDE OPEN FOR
THE EVENT...WITH PWATS PROGGED TO INCR IN THE 1-1.5" RANGE (300% OF
NORMAL) BY 12Z WED. THIS COUPLED WITH PROLONGED LLVL WAA OVR THE CAD
AND A STRONG UPSLOPE COMPONENT TO THE FLOW FOR A 6-12 HR PERIOD SHUD
RESULT IN WIDESPREAD 1.25-2.5" QPF BY WED AFTN (HIEST AMTS
CONCENTATED ALONG S-FACING SLOPES OF THE BLUE RIDGE).
THERE ARE A FEW CONCERNS WITH THIS EVENT. FIRST...MOST OF THE RIVER
BASINS ARE STILL RUNNING HIGH FROM LAST WEEK/S RAIN. SO THE CURRENT
QPF EXPECTED TUE NGT AND WED COULD CAUSE SOME FLOODING PROBLEMS.
SECOND...THE NAM AND GFS AGREE ON STRONG LLVL WINDS BOTH AHEAD OF
AND BEHIND THE COLD FRONT. RIDGE TOPS MAY HAVE WIND ADV CRITERIA
OVRNGT TUES NGT AS A SLY 50-60 KT H85 JET CROSSES THE AREA...THEN
LWA OR HIGHER GUSTS ARE POSSIBLE CWA-WIDE WEDNESDAY AFTN...WITH
W/SWLY WINDS 40-50 KTS ATOP BL IN STRONG CAA. THIRD...VERY STRONG
LLVL SHEAR IS EXPECTED LATE TUES NGT...AS THE WEDGE FRONT BEGINS TO
ADVANCE NWD. BASED ON THE CURRENT TIMING OF THE COLD FROPA (IN THE
MORNING)...I DON/T THINK THE WEDGE BNDRY WL BE ABLE TO ADVANCE NWD
MUCH AHD OF THE COLD FRONT AND MAY NOT REACH THE SRN TIER COUNTIES
BEFORE SHEAR AND INSTBY QUICKLY WANES. IN ANY CASE...THE SITUATION
FOR SOME EMBEDDED CONVECTION WITH DAMAGING WINDS OR ISOLD TORNADOES
SOUTH OF I-85 WILL NEED TO BE MONITORED.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 235 PM SUNDAY...WENT WITH HPC FAVORED GFS/ECMWF BLEND WED
NIGHT-SUN. H5 SHORTWAVE MOVES QUICKLY NE OF AREA WED NIGHT...LEAVING
ZONAL FLOW OVER REGION AS BROAD UPPER TROF MOVES SLOWLY ACROSS ERN N
AMERICA. SFC LOW ALSO TRACKS QUICKLY NE...LIMITING MOIST NW FLOW
INTO MTNS. STILL HELD ON TO SLIGHT CHC POPS OVER NC MTNS
OVERNIGHT...PSBLY MIXING WITH THEN TURNING TO LGT SNOW BEFORE
ENDING. SFC HI PRES BUILDS OVER AREA THU-FRI WITH PCLDY SKIES AND
NEAR AVG TEMPS THU...BLO AVG TEMPS FRI. SFC HI MOVES OFFSHORE FRI
NIGHT-SAT AS A LOW DEEPENS IN THE GULF AND TRACKS E TOWARD THE LOWER
SAVANNAH VLY. HI PRES CONT TO RIDGE IN FROM THE NE WITH WEDGE
DEVELOPING AND AS MOISTURE TRACKS NE...POPS WILL INCREASE FROM S TO
N FRI NIGHT. MODEL SOUNDINGS AND THKNS PROFILES HINT THAT A WINTRY
MIX WILL BE PSBL. KEPT IT SIMPLE ATTM WITH CHC RAIN MIXING WITH AND
TURNING TO SNOW OVERNIGHT...MAINLY NC MTNS...N FOOTHILLS AND NW
PIEDMONT...BUT A MIX APPEARS TO BE POSSIBLE INTO UPSTATE SC AS WELL.
WENT WITH CHC RAIN DURG DAY SAT WITH A SLIGHT CHC OF RAIN...PSBLY
MIXING WITH SNOW MTNS AND N ZONES SAT NIGHT. HIGH PRES BUILDS IN
FROM THE N SUN BUT DUE TO UNCERTAINTY THAT FAR OUT KEPT A SLIGHT CHC
OF RAIN ACROSS S TIER. TEMPS REMAIN BLO AVG.
&&
.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AT KCLT...HIGH LEVEL CIGS TO DIMINISH OVERNIGHT...BUT GIVE WAY TO
ENCROACHING STRATOCU DURING THE LATE NIGHT HOURS. THE NW EDGE OF
THE STRATOCU WILL BE CLOSE TO I-85 THIS MORNING...SO GIVEN THE
UNCERTAINTY...WILL KEEP THE BKN040 GOING...JUST LIKE THE GFS BUFKIT
DEPICTS. OTHERWISE...LIGHT NE WINDS THIS MORNING BECOMING LIGHT
SW BY THIS AFTERNOON...AS AC CIGS ENCROACHMENT FROM THE WEST THIS
EVENING.
ELSEWHERE...SCT-BKN LVFR LVL STRATOCU WILL OVERSPREAD THE PIEDMONT
THIS MORNING. OTHERWISE...5-6SM BR WILL BE PSBL AT KAVL/KHKY WHERE
THE SKY WILL BE CLEAR. VFR AND LIGHT WINDS FOR THE DAYTIME HOURS
FOLLOWED BY INCREASING ALTOCU THIS EVENING.
OUTLOOK...RAIN AND WIDESPREAD LOW CIGS AND VSBY ARE EXPECTED TUE
THROUGH EARLY WED AS A LOW PRESSURE SYSTEM FROM THE WEST BRINGS
ABUNDANT MOISTURE INTO THE AREA. DRYING IS EXPECTED MID TO LATE WEEK.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...HG/JDL
SHORT TERM...ARK
LONG TERM...RB
AVIATION...CSH/JDL
